<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<div>
    结果: <span></span>
</div>

<script>
    function f(n){

        //获取两个文本框  给元素添加id 浏览器会自动生成以下代码
        /*let i1=document.querySelector("#i1");
        let i2=document.querySelector("#i2");*/
        let s= document.querySelector("span");

        if(isNaN(i1.value)|isNaN(i2.value)){
            s.innerText="您输入有误!";
            return;
        }

        //s.innerText=i1.value*1+i2.value*1;
        //s.innerText=parseFloat(i1.value)+parseFloat(i2.value);
        switch (n){
            case 1:
                s.innerText=i1.value*1+i2.value*1;
                break;
            case 2:
                s.innerText=i1.value-i2.value;
                break;
            case 3:
                s.innerText=i1.value*i2.value;
                break;
            case 4:
                s.innerText=i1.value/i2.value;
                break;

        }
    }


</script>

</body>
</html>
